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High Mileage Subaru EJ251 Oil Filters #5258971 11/05/19 08:56 AM
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Hangman Offline OP
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Hello BITOG’ers!

Long time lurker, first time poster. Signed up specifically because I couldn’t find definitive information on what I’m looking for.

I own and daily drive a 2001 Forester (auto trans, S-trim, if any of that matters).

There’s a long running bit of “tribal knowledge” that Subaru’s MUST have a filter with a 23psi bypass. Wix 57055 for example.

I found a post here, though, stating that flow rate is more important. Could someone please explain this to me? I’m generally pretty comprehensible when it comes to these kinds of things, but this one is going over my head.

Any Subaru’ers know how particular EJ’s are about maintaining oil pressure, and as I’m approaching 200k on the original engine, I’d like to keep her alive as long as possible before doing a 207 swap.

While we’re on the subject, is there a “best” oil for a high mileage Subaru? It’s been getting either PP high mileage or M1 high mileage at 5k intervals, in 5-30.

Lastly, so as not to clutter up more threads, can anyone recommend a good oil filter relocation kit? My OEM exhaust manifold cracked, so I replaced it with an UEL header, and it is uncomfortably close to the oil filter, nigh touching, which I imagine isn’t great for oil temps!

Thank you for reading my blabbering!

Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259024 11/05/19 10:08 AM
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fozzdesy2001 Offline
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I miss my 01 Forester it ran about every type of oil filter that would fit with no problems. What I used the most were Subaru blue cans, WIX 57712 and Denso. I thought about a filter relocation kit but the engine bay is too crowded to find a good place for one. My XT had the filter in a horrible place placing it less than one inch away from the factory exhaust manifold that was below the filter on one side anything bigger than OEM or the WIX wouldn't fit. Explain "nigh touching" is it touching or just really close? I would not do extended oil change runs, just change the oil and filter every 5000 or so miles like your doing and you should be fine. The 2 oils you are using are excellent so if your happy your Subie will be happy. Stay on the lookout for head gasket problems.


2001 Subaru Forester S
Replaced with a 2006 Forester

2004 Subaru Forester XT
Death by deer. Replaced with 2003 Impreza Outback Sport (beater)
Re: High Mileage Subaru EJ251 Oil Filters [Re: fozzdesy2001] #5259065 11/05/19 11:13 AM
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Hangman Offline OP
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Originally Posted by fozzdesy2001
I miss my 01 Forester it ran about every type of oil filter that would fit with no problems. What I used the most were Subaru blue cans, WIX 57712 and Denso. I thought about a filter relocation kit but the engine bay is too crowded to find a good place for one. My XT had the filter in a horrible place placing it less than one inch away from the factory exhaust manifold that was below the filter on one side anything bigger than OEM or the WIX wouldn't fit. Explain "nigh touching" is it touching or just really close? I would not do extended oil change runs, just change the oil and filter every 5000 or so miles like your doing and you should be fine. The 2 oils you are using are excellent so if your happy your Subie will be happy. Stay on the lookout for head gasket problems.


Head gaskets have already been done. I figure a little after 200k I’m going to re-do all the gaskets, water pump, and timing components, as I’m not sure WHEN they were done.

By “nigh touching”, I mean I have to loosen the head studs holding the Header on in order to remove the oil filter. It may be touching by a smidge. Mine is a 2001 S Auto with the Winter package; one of those options included a factory “oil cooler”, which is really just a sandwich plate off the block, which lowers the oil filter down about 2.5-3”, making it rest on the header. Right now it has a M1 108 on it. I’m thinking of switching to the Wix 57055 as it has similar dimensions with better flow and bypass.

What exactly does the bypass rating mean? At anything over 23psi, the oil bypasses the filtering media completely?

Last edited by Hangman; 11/05/19 11:18 AM. Reason: Dyslexia
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259127 11/05/19 12:26 PM
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geeman789 Offline
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You have 200 k on the engine ... what have you been using ? Because they seem to be working .

Your Subaru does not NEED an oil filter with the higher than average 23 psi by-pass spec. And FLOW is not an issue with almost any modern oil filter, as most flow far more oil than your cars oiling system will ever use.

Subaru DOES spec a higher by-pass relief pressure than most car makers. WHY they do has been debated for many many years, with no definitive answer.

Some guesses as to why include:

1) A higher flow oil pump, which in some situations ( cold oil, higher rpm's ) can push the filter into by-pass mode more frequently.

2) The use of fine screen banjo bolts in turbo models, which have been prone to clogging on poorly maintained cars. See above ... more by-pass events means the possibility of more unfiltered oil hitting the screens, possibly leading to clogging and oil starvation to the turbo bearing.

IMO, the higher by-pass spec seems more important for the turbo cars.

The by-pass valve on the oil filter is there to prevent excessively high pressure differentials caused by cold, thick oil, completely clogged filter media, or high rpm / max oil flow from damaging the filter element or blowing out the gasket, and to prevent excessive oil pressure drops downstream of the oil filter. The oil pump will ALWAYS pump the oil ... and it will go SOMEWHERE. The by-pass valve is supposed to be the path of least resistance PAST a certain pressure differential. The valve is not an ON / OFF switch. It is a spring loaded valve that will open and close to a variable degree depending on the pressure differential. On a cold winter start it might be open for a few minutes straight until oil temps warm up. At 5-6000 rpm hot, the valve might start to crack open a little as oil pump volumes start to max out, then close as rpms drop down again.

The higher by-pass spec delays the valve from opening, or prevents it from opening at all. On that cold winter morning, the by-pass valve might open a 1/2 second later. And when hot, that higher by-pass pressure may delay the valve from opening at 5000 rpm, only starting to open at 6000 rpm.


My non-turbo Impreza has used many different brands of oil filters, some with the correct by-pass spec, others without it. Car runs perfect after 100 k miles ...

That being said, WIX filters seem to be well constructed, and are available with the correct by-pass spec., so I use these most often. I also have a Fram Racing HP-17, which has the correct spec. by-pass as well.


https://www.bobistheoilguy.com/foru...0413/napa-gold-7055-cut-open#Post5250413

https://www.bobistheoilguy.com/foru...ing-hp17-cut-open-w-pictures#Post5246161


2011 SUBARU Impreza 5-door manual / 2016 HONDA Pilot / 2011 MAZDA 2 auto
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259130 11/05/19 12:31 PM
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geeman789 Offline
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This is what one style of a by-pass valve looks like ... just a button on a spring. A 23 psi by-pass valve just has a slightly stiffer spring than a 12 psi one ...

[Linked Image]


2011 SUBARU Impreza 5-door manual / 2016 HONDA Pilot / 2011 MAZDA 2 auto
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259131 11/05/19 12:34 PM
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krismoriah72 Offline
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I have a 2001 Forester with near 450K. I bought it at 350K with a blown head gasket for $150. (note the speedometer was not working when i got it, i was told it wasnt working for a couple of years).. I fixed it but it could very well have 600K on it.


The first 350K were put on by sales reps for petroleum products to coal mines and deep rural areas. Oil used was Chevron Supreme dino and Valvoline Dino with Napa silver filters. I think their OCI was 7500K if i remember right.

My 100K oils used were anything on clearance and alot of Smittys from Kmart. Filters were mostly Supertech.

Engine has no known oil related issues, still starts as good as a new one.

I have given up on driving it and need to sell it.. I do wish that i could somehow buy one brand new and start over with zero miles...

I doubt running synthetic oils or Fram XGs instead of dino and jobber filters would have made any difference in mines life... just a well built engine with a poor choice of head gaskets.

Re: High Mileage Subaru EJ251 Oil Filters [Re: geeman789] #5259134 11/05/19 12:36 PM
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jbutch Offline
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Originally Posted by geeman789
You have 200 k on the engine ... what have you been using ? Because they seem to be working .

Your Subaru does not NEED an oil filter with the higher than average 23 psi by-pass spec. And FLOW is not an issue with almost any modern oil filter, as most flow far more oil than your cars oiling system will ever use.

Subaru DOES spec a higher by-pass relief pressure than most car makers. WHY they do has been debated for many many years, with no definitive answer.

Some guesses as to why include:

1) A higher flow oil pump, which in some situations ( cold oil, higher rpm's ) can push the filter into by-pass mode more frequently.

2) The use of fine screen banjo bolts in turbo models, which have been prone to clogging on poorly maintained cars. See above ... more by-pass events means the possibility of more unfiltered oil hitting the screens, possibly leading to clogging and oil starvation to the turbo bearing.

IMO, the higher by-pass spec seems more important for the turbo cars.

The by-pass valve on the oil filter is there to prevent excessively high pressure differentials caused by cold, thick oil, completely clogged filter media, or high rpm / max oil flow from damaging the filter element or blowing out the gasket, and to prevent excessive oil pressure drops downstream of the oil filter. The oil pump will ALWAYS pump the oil ... and it will go SOMEWHERE. The by-pass valve is supposed to be the path of least resistance PAST a certain pressure differential. The valve is not an ON / OFF switch. It is a spring loaded valve that will open and close to a variable degree depending on the pressure differential. On a cold winter start it might be open for a few minutes straight until oil temps warm up. At 5-6000 rpm hot, the valve might start to crack open a little as oil pump volumes start to max out, then close as rpms drop down again.

The higher by-pass spec delays the valve from opening, or prevents it from opening at all. On that cold winter morning, the by-pass valve might open a 1/2 second later. And when hot, that higher by-pass pressure may delay the valve from opening at 5000 rpm, only starting to open at 6000 rpm.


My non-turbo Impreza has used many different brands of oil filters, some with the correct by-pass spec, others without it. Car runs perfect after 100 k miles ...

That being said, WIX filters seem to be well constructed, and are available with the correct by-pass spec., so I use these most often. I also have a Fram Racing HP-17, which has the correct spec. by-pass as well.


https://www.bobistheoilguy.com/foru...0413/napa-gold-7055-cut-open#Post5250413

https://www.bobistheoilguy.com/foru...ing-hp17-cut-open-w-pictures#Post5246161


This is a very well written explanation, good post geeman789!


2015 Forester XT @ 100k km
Current fill: Rotella T6 Multi Vehicle 5w-30 with Fram Ultra XG7317
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259198 11/05/19 02:25 PM
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Ignatius Offline
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I have thought this over and done a lot of research to include asking questions of people who know the engineering when I worked for Subaru. The conclusion I have come to would be to simply ask why use any filter other than the OEM if you have any concerns? It is spec'ed for the bypass and flow rate, quite literally engineered specifically for Subaru applications.

All other oil filters have arguements for and against them to include:

Wix: Has bypass spec but max flow rate is limited to 10 gallons per minute, Subaru requires 14.5 gallons per minute.

Fram: Has flow rate but not bypass spec except on PH9715 and HP series.

I don't want to go round and round arguing with anyone because every debatable aspect has been debated extensively without definive answers. Again why use something other than a Subaru OEM oil filter if you have concerns?


2018 Subaru Outback Limited - 75,000 miles
2018 Subaru Outback Premium - 30,000 miles
2012 Hyundai Accent GLS - 93,000 miles
2005 Dodge Sprinter 3500 - 161,000 miles
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259207 11/05/19 02:44 PM
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2018 RAM 1500 SLT 5.7L
Formula Shell Conventional 5w20 - Fram Tough Guard


Disabled US Army Vet
OEF 2013-2014
Re: High Mileage Subaru EJ251 Oil Filters [Re: Ignatius] #5259228 11/05/19 03:16 PM
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geeman789 Offline
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Originally Posted by Ignatius


I have thought this over ...



We know ...

You seem to be hung up on the oil pump max flow volumes. Figures that came out of a service manual, not an engineering blue print, and may, or may not be accurate.

At 14.5 gpm of oil flow, the oil filter will not be the primary restriction, the ENTIRE oil circuit will be. The oil pump will build pressure up to the OIL PUMP high pressure safety valve threshold, dumping the excess oil back into the sump. Some cars use oil filters with no by-pass valve at all.

The oil pump is designed to always flow MORE oil than the engine oil circuit requires. Because less oil than needed is BAD. That excess oil doesn't go thru the filter ...


2011 SUBARU Impreza 5-door manual / 2016 HONDA Pilot / 2011 MAZDA 2 auto
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259232 11/05/19 03:34 PM
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geeman789 Offline
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Originally Posted by Hangman
Hello BITOG’ers!

While we’re on the subject, is there a “best” oil for a high mileage Subaru? It’s been getting either PP high mileage or M1 high mileage at 5k intervals, in 5-30.



The EJ non-turbo engines aren't real picky about oil. There is no direct injection to fuel dilute the oil, or timing chains to chop it up ... or turbo's to cook it.

Clean oil from a reputable brand is far more important than a specific brand or flavour. PP and M1 are both solid oils. I use both, depending on what is on sale. Don't over think it !


2011 SUBARU Impreza 5-door manual / 2016 HONDA Pilot / 2011 MAZDA 2 auto
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259255 11/05/19 04:22 PM
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Hangman Offline OP
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I have received SO MUCH more information and SO MUCH more valuable input than I could have EVER imagined.

Thank you ALL for your answers.

So, in essence, the bypass acts just like a turbo’s wastegate; sees too much pressure, begins to open. Am I understanding that correctly?

I was more worried about using a filter with a bypass rating LOWER than Subaru’s spec’d 23psi. The M1-108 I’m using is only rated at (top of my head) 18psi. I had to use it because my aftermarket header prevents the use of a large-frame filter. I’ve since found that the Wix 7705 has the same form factor with more Subaru appropriate specs, and will be switching.

I don’t want to buy the OEM Subaru blue filters because they’re outrageously expensive, and their form factor doesn’t fit with an aftermarket header.

Speaking of such...anyone recommend a quality oil filter relocation kit?

Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259281 11/05/19 05:05 PM
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Lubener Offline
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I get Subaru blue cans for slightly under five dollars from my Subaru dealer. I wouldn't call that outrageously expensive.


The "thinking" man's friend.
Re: High Mileage Subaru EJ251 Oil Filters [Re: Lubener] #5259345 11/05/19 06:38 PM
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Ignatius Offline
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Originally Posted by Lubener
I get Subaru blue cans for slightly under five dollars from my Subaru dealer. I wouldn't call that outrageously expensive.


I am with you, we're talking about a car part that one can buy with one small bill. Even the more expensive oil filters like Amsoil can be had for less than $20. I like saving money but I don't think it is worth my time and headache to get worked up over a few dollars one way or the other.


2018 Subaru Outback Limited - 75,000 miles
2018 Subaru Outback Premium - 30,000 miles
2012 Hyundai Accent GLS - 93,000 miles
2005 Dodge Sprinter 3500 - 161,000 miles
Re: High Mileage Subaru EJ251 Oil Filters [Re: Hangman] #5259360 11/05/19 06:46 PM
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geeman789 Offline
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Originally Posted by Hangman


So, in essence, the bypass acts just like a turbo’s wastegate; sees too much pressure, begins to open. Am I understanding that correctly?

I was more worried about using a filter with a bypass rating LOWER than Subaru’s spec’d 23psi. The M1-108 I’m using is only rated at (top of my head) 18psi. I had to use it because my aftermarket header prevents the use of a large-frame filter. I’ve since found that the Wix 7705 has the same form factor with more Subaru appropriate specs, and will be switching.



The WIX 7712 is the " short " Subaru spec filter. The 7055 is the " tall " Subaru spec filter. The 7712 is about 1 inch shorter.

Like you stated, the oil filter by-pass valve opens when there is too much pressure difference. For example, cold oil is way thicker, and will resist flowing thru the filter media, creating more pressure than normal. The by-pass valve will start to open once pressure reaches the design spec. So, some oil goes thru the filter media, but some oil will flow unfiltered thru the by-pass valve.

A lower by-pass valve setting means POSSIBLY more by-pass events, and LONGER by-pass events, and more unfiltered oil passing thru to the engine. Fewer by-pass events are better. But, a bit of unfiltered oil IS WAY BETTER than not enough oil. A by-pass valve helps prevent the filter media from tearing or ripping, keeps oil pressure from blowing the filter gasket, and most importantly, lets oil get thru to the engine.

And, judging by how little junk there usually is in a filter ( cut one open and look ... ) , by-passed oil isn't really very dirty, and does't seem to hurt the engine at all. All oil filters will be in by-pass some of the time, usually on those cold start mornings.


2011 SUBARU Impreza 5-door manual / 2016 HONDA Pilot / 2011 MAZDA 2 auto
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